Manufacture of composites containing a thermally shaped inorganic fiber form

ABSTRACT

THE PRESENT INVENTION REALTES TO A METHOD OF SHAPING AMORPHOUS FIBERS ABOUT ONE OR MORE TRANSVERSE AXES BETWEEN THE ENDS OF EACH FIBER COMPRISING FORMING THE FIBERS INTO A SHAPE AND THEN HEATING THE SHAPED FIBERS AT A TEMPERATURE OF ABOUT 200*F. TO ABOUT 1200*F. FOR A TIME OF ABOUT 1 TO ABOUT 24 HOURS. UPON COOLING, THE SOPROCESSED FIBERS RETAIN SUBSTANIALLY THE SAME FORMED AND HEATED FIBER CONFIGURATION. THE SO-SHAPED FIBERS CAN BE EMPLOYED FOR USES SUCH AS REINFORCEMENT OF CAST METAL, CERAMIC, AND PLASTIC SHAPES.

*United States Patent MANUFACTURE OF COMPOSITES CONTG A THERMALLY SHAPED INORGANIC FIBER FORM Garth D. Lawrence, Midland, and Jack J. Ott, Hemlock,

Mich., assignors to The Dow Chemical Company, Midland, Mich. No Drawing. Filed Aug. 13, 1971, Ser. No. 171,763

Int. Cl. B21f 3/04; B22d 19/02; C04b 35/72 US. Cl. 264-257 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to a method of shaping amorphous fibers about one or more transverse axes between the ends of each fiber comprising forming the fibers into a shape and then heating the shaped fibers at a temperature of about 200 F. to about 1200 F. for a time of about 1 to about 24 hours. Upon cooling, the soprocessed fibers retain substantially the same formed and heated fiber configuration. The so-shaped fibers can be employed for uses such as reinforcement of cast metal, ceramic, and plastic shapes.

BACKGROUND OF THE INVENTION This invention relates to forming and more in particular to the forming of amorphous fibers at elevated temperatures.

Amorphous fibers such as boron, silicon carbide coated boron, glass fibers and the like have been used to reinforce structural metal articles, i.e., metal-fiber composites. Usually such fibers are produced and employed as straight lengths and, consequently, are generally unsuitable to reinforce an article of a complex design. It has been commonly believed that forming of such filaments at room temperature was not possible because of the tendency of the filaments to be brittle and fracture before adequate plastic deformation could be achieved. It also has been thought that such fibers are elastic at elevated temperatures below the minimum hot working temperature, i.e., the temperature of recrystallization, and, therefore, could not be permanently shaped without significantly altering the tensile properties.

It is an object of this invention to provide a method of forming amorphous fibers.

It is another object of this invention to provide a method for forming amorphous fibers at temperatures below the recrystallization temperature of the fiber without significantly altering the tensile properties.

Other objects and advantages of this invention will become apparent during the course of the following discussion.

SUMMARY OF THE INVENTION The hereinbefore described objects have been achieved in a method of shaping an amorphous fiber comprising elastically forming the fiber into a shape at least at one point between the ends thereof. The formed fiber is restrained and maintained in said shape while heated at a temperature of about 200 F. to about 1200 F. for a time sufiicient to permanently deform the fiber. The deformed fiber is then cooled to a temperature lower than the temperature to which it was heated before being released from the restrained shape. The cooled fiber can be effectively used as, for example, a reinforcing member in a composite composed of at least one other substance such as a plastic, ceramic, or metal.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An amorphous fiber or filament of a substance such as boron, silicon carbide coated boron, a tungsten cored 3,775,530 Patented Nov. 27, 1973 "ice boron filament, a tungsten cored boron filament with a coating of silicon carbide, glass and the like can be formed into a shape without plastically deforming the fiber and heated to a temperature of about 200 F. to about 1200 F. for at least about one hour and preferably about one hour to about 24 hours to permanently deform the fiber. Preferably heating to permanently deform the fiber is carried out at a temperature of from about 300 F. to about 1200 F. and more preferably of from about 500 F. to about 1200 F. The fibers are formed at a temperature below about the recrystallization temperature of the fiber. After heating, the fiber is preferably cooled to below about 300 F. and more preferably below about 200 F. before releasing the fiber from the restrained configuration. Processing the amorphous fibers in this manner will produce a permanent set of simple or complex configurations in the fiber.

Deterioration or oxidation of the fiber during the heating step can be prevented through the utilization of an atmosphere inert to the filament such as a vacuum, helium, neon, argon and the like.

In performing the method of the present invention, the fiber can be formed by, for example, winding the fiber around a stationary body of a desired configuration, for example, circular, elliptical, rectangular, hexagonal, and the like shaped mandrels. Preferably the mandrel has a curved surface. Such forming can be carried out at a temperature up to the recrystallization temperature of the fiber without plastically deforming the fiber. While maintaining the fiber in the formed configuration, the fiber is heated within the above described temperature range for the desired time. Upon cooling, the fiber retains the general shape into which it was formed; relaxation or spring-back of the cooled fiber can be compensated for by initially forming the fiber into a tighter or more restrictive, although similar, configuration than the final shape desired. The fact that amorphous fibers can be permanently deformed by the method of the present invention is unexpected since it has been heretofore believed that such fibers do not creep or plastically deform at temperatures below about 1200 F.

In a particular embodiment, the above described cooled shaped fiber can be inserted and preferably detachably mounted in a casting mold cavity. Subsequent to such insertion, the mold cavity contacting the shaped fiber can be filled with a solidifiable substance, for example; a fluid such as a ceramic, plastic, molten metal and the like or a slurry including, for example, particulate ceramic, plastic, metal and the like. The fluid can then be solidified around the shaped fiber to produce a fiber reinforced article of simple or complex design. When the mold cavity is filled with the fluid, and especially a molten metal, the fiber and mold cavity is preferably heated and dried prior to filling the cavity with the fluid. Preferably such drying is carried out at a temperature of about 200 F. to about 1400 F. in a vacuum of less than about one millimeter of mercury for a time of at least about one hour.

The following examples are illustrative of the present invention.

Examples 1-3 Straight filaments with a 0.5 mil diameter tungsten core, a 1.75 millimeter coating of vapor deposited boron and a 0.2 millimeter second coating layer of vapor deposited silicon carbide were elastically bent around a 0.75 inch diameter mandrel, clamped in the bent shape and then individually vacuum heated for various times and temperatures. Heating for one hour at 500 F. and then cooling to F., before unclamping the filament, produced a filament which retained a nine inch radius of curvature. A filament heated sequentially for one hour at 500 F. and then one hour at 800 F. retained a three inch radius of curvature upon cooling. The radius of curvature produced was reduced to two inches when the filament was sequentially heated for one hour at each 500 F., 800 F., and then 1100 F.

Examples 4-7 Straight filaments substantially the same as described in Example 1 were elastically formed and clamped around a inch diameter mandrel and individually vacuum heated at various temperatures for 24 hours. Upon cooling to room temperature the filaments were released and found to have retained a permanent set as follows:

200 F. treatment7.5 inch radius; 300 F. treatment4 inch radius; 400 F. treatment-2.3 inch radius; and 600 F. treatment-1% inch radius.

Example 8 A straight filament having a 0.5 millimeter diameter tungsten core wire and a 1.75 millimeter coating of vapor deposited boron was elastically wound and removably fixed around a 2.25 inch diameter mandrel and vacuum heated at a temperature of 800 F. for 16 hours. The filament was cooled to room temperature and removed from the mandrel and found to have retained a three inch radius of curvature.

Example 9 A straight filament of Pyrex glass was bent into a radius of 0.63 inch and maintained in that position for 16 hours in a vacuum furnace at a temperature of 500 F. The filament had retained a eight inch radius of curvature after it had been cooled to room temperature and removed from the mandrel.

Example 10 The shaped filament of Example 2. with a three inch retained radius was clamped in a straightening jig, vacuum heated for 16 hours at 800 F. and cooled to room temperature before being released from the jig. The filament was satisfactorily straightened into substantially the same shape as it was in prior to the forming carried out in Example 2. The restraightened filament was tested to determine the utilmate tensile strength; it was found that this physical property was statistically unchanged from that of the received, straight filament of Example 2. The as received straight filament was found to have an average tensile strength of about 349,000 p.s.i. and the restraightened filament had an average tensile strength of 341,000 p.s.i.

Example 11 After forming the filament substantially the same as described in Example 1, the formed filament was inserted and fixed in a graphite mold cavity. The mold and inserted shaped filament were dried at a temperature of 1400 F. for a period of 16 hours in a vacuum of less than about one millimeter mercury. After drying, the mold and filament were cooled in the vacuum furnace to a temperature of 1000 F. The mold cavity was then filled with dry air and immersed in molten magnesium, at a temperature of 1400 F., and maintained therein for a period of one hour. The mold cavity filled with magnesium substantially as described in US. Pat. 3,364,976. Upon removal from the molten magnesium and cooling to room temperature, the mold was opened to afford removal of a solidified magnesium composite shape having filament reinforcements embedded within the casting.

Comparative example A crystalline silicon carbide filament 'was elastically bent and removably fixed around a 0.75 diameter mandrel. The so-fixed crystalline filament was heated in a vacuum for 1 hours at 500 F. and then one hour at 800 F. The filament was removed from the mandrel after cooling to room temperature and found to have retained the original shape.

It can be readily seen from the examples that the present invention can be employed to produce a permanent set in amorphous fibers. As shown in the comparative example, this technique is not effective in shaping crystalline fibers, such as silicon carbide.

What is claimed is:

1. A method of making a composite containing an amorphous fiber shape comprising:

(a) elastically forming a fiber selected from the group consisting of boron, silicon carbide coated boron, boron coated tungsten, tungsten cored boron filament having a silicon carbide coating, and glass into a shape at least at one point between the ends thereof;

(b) restraining and maintaining the fiber in the shape;

(c) heating the so maintained fiber in a substantially monoxidizing atmosphere at a temperature and for a time sufiicient to permanently deform the fiber, the temperature being within the range of from about 500 F. to about 1200 F.;

(d) cooling the heated shaped fiber;

(e) releasing the cooled restrained fiber;

(f) inserting the cooled fiber into a casting mold cavity;

(g) filling the cavity with a solidifiable substance; and

(h) solidifying the substance into a fiber reinforced article.

2. The method of claim 1 including heating the formed fiber for at least about one hour.

3. The method of claim 1 including heating the formed fiber for about one hour to about 24 hours.

4. The method of claim 1 wherein the fiber is formed by winding the fiber around a curved mandrel.

5. The method of claim 1 wherein the fiber is heated in an atmosphere inert to the fiber.

6. The method of claim 1 wherein the fiber is selected from the group consisting of boron, silicon carbide coated boron, boron coated tungsten and silicon carbide and boron coated tungsten.

7. The method of claim 1 wherein the solidifiable substance is selected from the group consisting of a ceramic, plastic and molten metal.

8. The method of claim 1 wherein the cavity is filled with molten magnesium.

9. The method of claim 1 wherein the solidifiable substance is a slurry including particulate selected from the group consisting of a ceramic, plastic and metal.

10. The method of claim 1 wherein the fiber is selected from the group consisting of boron, silicon carbide coated boron, and glass.

References Cited UNITED STATES PATENTS 3,426,115 2/1969 Taber 264339 3,103,722 9/1963 Whitehurst et al 164-97 3,595,946 7/1971 et al 26429 3,462,289 8/ 1969 Rohl et a1 264-Dig. 19

JOHN H. MILLER, Primary Examiner US. Cl. X.R.

16498; 264-60, 285, 332, 339, Digest 19 qgz ge UNITED STATES PATENT oTTTtE CERTIFICATE @F CQRRECTWN Patent No. 3,775,530 Dated November 27, 1 7

Inventor(s) arth D. Lawrence, Jack J. Ott

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2, line 45 change the word "contacting" to ---containing--. 2

Column 3, line 44, change "utilmate" to -ultimate-..

Column 4, line 2, change "hours"to --hour- Column 4, line 22, change "monoxidizing" to --nonoxidizing-.

Signed and sealed this 17th day of September 1974,

(SEAL) Attest: v

McCOY M. GIBSQN JR. 0.. MARSHALL DANN Atteating Officer Commissioner of Patents 

